1. Field of the Invention
This invention pertains to closures, and more particularly to closures for fragile containers in which is found an accumulation of pressurized free gas.
2. Description of the Prior Art
The modern carbonated beverage is composed of carbonated water, a sweetning agent, acid, flavor, color, and a preservative. The characteristic pungent taste or "bite" associated with carbonated beverages is contributed by carbon dioxide solute, which also inhibits the growth of bacteria. In addition to the solute form, carbon dioxide is usually found along with air as a free gas in a space at the top of the container, typically occupying about 25 cc. of a 10 ounce bottle. The presence of the free gas creates an explosion hazard in fragile containers such as glass bottles should the bottle break, causing the glass fragments to scatter at high velocity. The danger is aggravated at high beverage temperatures at which the water solubility of carbon dioxide is reduced and free gas is driven out of solution to add to the explosive energy, which energy is a function of free gas quantity and pressure. It has proven mechanically difficult to completely fill the bottle and thus remove the free gas, and even if this was accomplished thermal expansion of the beverage within could rupture the bottle should it and its contents become heated. Thermal expansion is not an urgent problem in containers with a relatively large volume of free gas, as 10 ounces of water will expand by only about 5 cc. when heated from 32.degree. to 140.degree. F., the maximum opposite temperature extremes usually encountered by carbonated beverages, and by about 4.5 cc. from room temperature of 70.degree. to 140.degree. F. It becomes critical, however, at the small free gas volumes associated with completely or nearly completely filled containers.
Bottle closures are known to the art that provide means for relieving free gas pressure build-up inside a bottle, such as flexible membranes or bellows for expanding the volume available to the gas under pressure. These closures, however, do not attack the basic safety problem created by the mere existence of a significant quantity of free gas in a fragile container, even at normal temperatures.